1. Field of the Invention
The present invention relates to a resin package with a three-dimensional circuit formed therein which is used for mounting face down a solid-state image sensor such as a CCD (charge couple device) and a CMOS (complementary MOS) device.
2. Description of the Background Art
In the past, a hollow resin package as illustrated in FIG. 1 has been used for the package for mounting a solid-state image sensor. After a solid-state image sensor 1 is mounted in the hollow section 5 of this hollow resin package, the inner lead 2 and the solid-state image sensor 1 are electrically connected by bonding them by means of thin wire 4 such as gold wire, and a transparent lid 6 is bonded to the top surface of the resin section 3 so that the hollow section 5 is hermetically sealed.
On the other hand, as there has been a growing demand in recent years for a smaller and thinner package for housing a solid-state image sensor, various methods are beginning to be used under which a solid-state image sensor is mounted in the form of a bare chip. Among such methods is a box-type molded article obtained by making use of the MID (molded interconnect device) technique, a three-dimensional circuit forming technology as illustrated in FIG. 2. Under this method, after a molded article having an opening 8 in the bottom of a box is molded by the injection molding method, a circuit 7 is formed on a surface of the resin section 3 inside the aforesaid box-type molded article, and then a solid-state image sensor 1 is mounted face down onto the circuit 7 formed near the opening 8. Japanese Laid-open Patent Publication No. 2002-280535 gives a description of a technique using a box having an opening in its bottom and a lens tube as an integral part of the box. The integral part is called the lens mounting seat, and the Japanese Laid-open Patent Publication proposes a technique of forming a wiring pattern by plating it directly onto the bottom of the lens mounting seat.
In this case, there are many methods based on the MID technique available for forming a circuit on the resin surface. For example, in the case of the 2-shot method, a resin on which a circuit can be formed is injection-molded first, and then after the molded article is set in another mold, the outer shape is over-molded. After that, the surface of the resin on which a circuit can be formed is subjected to plating so that a circuit is formed. Furthermore, the one-shot method is another method for forming a circuit, under which the deposition of a thin copper coating on the resin surface by means of sputtering or the application of a thin copper coat to the resin surface by means of electroless plating is followed by resist coating, exposure/development, copper etching, resist removal and then plating of nickel or gold onto the area in which a circuit has been formed.
Aside from the method of forming a circuit in the aforesaid box-type molded article, a different method is proposed as described in Japanese Laid-open Patent Publication No. 2002-204400 under which a circuit pattern of an image module with lens is formed by means of a lead frame.
The conventional hollow package made of resin tends to be large and thick overall because it is so structured that a solid-stage image sensor is mounted in the hollow package which is hermetically sealed by means of a transparent lid. Because of this, this form of package is beginning to fail to meet the recent demand for a smaller and thinner package. In addition to that, since the image sensor and the inner lead are bonded by means of gold wire, the light reflected diffusely at the bonding wire enters the image sensor, causing the distortion of the image in some cases.
On the other hand, the method under which a solid-state image sensor is mounted face down in a molded article on the surface of which a three-dimensional circuit has been formed by the MID technique does not need such box as used in a hollow package because a bare chip is mounted, offering the advantage of making the package as a whole smaller and thinner. Furthermore, since there is no bonding by means of gold wire, there is no occurrence of diffused reflection at the wire, which in turn causes no occurrence of a distorted image.
However, the method under which a three-dimensional circuit is formed in a resin molded article by the MID technique requires that in the case of the 2-shot method, two molds should be used and the resin surface should be roughened after the resin on which a circuit can be formed is molded in the first shot so that the adhesive strength of the resin interface is improved. On the other hand, under the 1-shot method, only one mold is required, but the process for forming a circuit involves many steps, such as thin coat plating, resist coating, exposure/development, copper etching, and resist removal. Both of these methods have a disadvantage of high manufacturing cost due to the complex processes.
In addition, Japanese Laid-open Patent Publication No. 2002-204400 proposes a method under which a modular circuit for an image sensor with lens is formed by use of a lead frame. But this method requires that after completion of insert molding, the outer lead should be bent complexly to follow the periphery of the box-type molded article because the lead has not been bent in advance.
With the objective of resolving the above problems experienced in producing a small and thin solid-state image sensing device, the present invention relates to a box-type package made of resin for mounting a solid-state image sensor in which a three-dimensional circuit is formed. The box-type resin package comprises a resin section and a lead embedded in the resin section. The resin section has a bottom surface with an opening for allowing light to pass so that a solid state image sensor may be mounted face down on the bottom surface. In the package, a three-dimensional circuit is formed which has a lead formed from a conductive metal plate making electrical conductance possible. The lead has an inner lead, an outer lead, and a bent lead section. The top surface of the inner lead is exposed on the inside bottom surface in the vicinity of the opening, and the top surface of the outer lead and the edge of the outer lead following a bent section of the lead are exposed on the side wall top surface of the resin section and the top edge of the side wall side surface of the resin section, respectively, with all the parts of the lead other than the exposed surfaces and edge of both ends being embedded in the resin section.
The aforesaid conductive metal plate can be formed into a circuit in the box-type resin package by bending three-dimensionally a lead frame generally used in semiconductor encapsulation. Under this technique, a three-dimensional circuit is formed by use of a lead frame, and therefore this technique does not require going through a complex process such as the MID method, making the formation of a circuit possible at low cost. Specifically, a resin package for a solid-state image sensor can be obtained easily by setting in a mold a lead frame having a three-dimensional structure with the lead in a bent condition, carrying out resin molding and then cutting off the lead protruding from the surface of the edge of the resin molded article to separate it from the lead frame after the thin resin flashes remaining on the lead surface are removed.
The aforesaid solid-state image sensor to be mounted in the box-type resin package is a light-receiving type semiconductor device such as CCD and CMOS.
Furthermore, the resin for use in the molding of the box-type resin package is preferably a thermosetting resin such as epoxy resin, phenol resin, polyimide resin, unsaturated polyester resin and silicone resin or heat-resistant thermoplastic resins such as liquid-crystal polymer, polyphenylene oxide, polyphenylene sulfide (PPS) resin, polysulfone and polyamide-imide-polyacrylsulphone resin. Out of these, epoxy resin, polyimide resin, PPS, etc. are especially preferable. For polyimide resin, polyaminobismaleimido, polypyromelliteimide and polyimide resin such as polyether may be used.
An inorganic filler is preferably added to these heat-resistant resins. Examples of such inorganic filler include heat-resistant inorganic fillers such as silica powder, alumina powder, silicon nitride powder, boron nitride powder, titanium oxide powder, silicon carbide powder, glass fiber and alumina fiber. Out of these, silica powder, alumina powder, silicon nitride powder and boron nitride powder are more preferable because the use of such inorganic filler will cause shrinkage after the molding of the resin package to be isotropic. The particle size of such inorganic filler is preferably 0.1 to 120 xcexcm, more preferably 0.5 to 60 xcexcm from the viewpoint of flowability at the time of molding. Such inorganic filler is added to heat-resistant resin in the amount of preferably 40 to 3,200 parts by weight, more preferably 100 to 1,150 parts by weight, to 100 parts by weight of the heat-resistant resin. Further, the heat resistant resins may contain a hardener, a hardening accelerator and a coupling agent in addition to these inorganic fillers.
The lead is provided in the form of a lead frame and is selected from among copper, iron, aluminum and any alloy of these. The lead is preferably formed from 42 alloy or copper alloy. The surface of the lead frame does not need to be treated but may be treated totally or partially as required. For example, the lead frame may be plated with gold, silver, nickel, solder, etc.